Load carrying bodies were an integral part of trucks from their earliest beginnings, prominently including the open top box type especially useful for carrying particulate material such as dirt, sand, gravel, and many other heavy semi-fluid materials. Shortly thereafter the box type body was equipped with a pivotally attached tail gate selectively locked to retain a load or released to discharge a load, and the box type body was pivotally mounted at the rear end of a truck and provided at its front end with lifting means to raise and tilt the box type body, thereby creating the universally used dump truck.
This arrangement for discharging a load quickly and easily naturally worked best when the bottom and sides of the truck body had smooth uninterrupted inside surfaces without projecting obstructions, as was generally the case.
However trucks got larger, loads got much larger and much heavier and had to be lifted higher to be unloaded, often on soft or sloping surfaces or under overhead obstructions where their use was difficult or downright dangerous.
As long as fifty years ago efforts were made to improve on the truck body configuration and mode of operation summarized above, as in U.S. Pat. No. 1,927,653 issued Sept. 19, 1933 to W. G. Wehr, and more recently in U.S. Pat. No. 3,953,170 issued Apr. 27, 1976 to James O. Webb, each disclosing a truck body fixedly mounted horizontally on a truck or truck trailer, provided with a load pusher or ejector initially located toward the front of the truck body when it is loaded, and later moved lengthwise of the truck body to discharge the load from its rear end.
Large trailer truck bodies incorporating various features generally corresponding to those described and illustrated in U.S. Pat. No. 3,953,170 are presently in use commercially.